British Prime Minister David Cameron and French President Nicolas Sarkozy signed two military cooperation treaties at Lancaster House in central London on Tuesday, heralding a new, closer and cheaper era of military cooperation between the two nations.

In the second treaty, nuclear weapons research and nuclear warhead testing facilities will be pooled, with a new facility being built in France, surmounting the closely-guarded manner in which both nations have protected their nuclear secrets from each other.

President Sarkozy said in a press conference after the treaty signing that this cooperation showed a "level of confidence between our two nations unequalled in history".

For both of the European nations, which between them account for 50 percent of European military equipment spending and 65 percent of military research, the goal is to reduce military costs at a time of acute cost-cutting in their government budgets.

For both nations, one of the aims of the treaty is to bolster their global military capabilities in a post-financial crisis period when they can no longer afford to maintain independent forces of a significant size across all three armed forces which can be deployed anywhere in the world.

Both nations are also permanent members of the United Nations Security Council and have an interest in maintaining their status in the top rank of military nations over the coming decades, and the treaty has a lifespan of 50 years.

Britain and France agreed to form a British-French carrier group, rotating the carrier between the British ship and the French ship, and to fly each other's planes from the carriers. This will require a change to British carrier designs.

Cameron said the treaty would see British and French armed forces "cooperating more closely than ever before". He described Britain and France as "natural partners", and that in a period of budget cutbacks cooperation would allow both nations to "expand our sovereign capability, even at a time when resources are tight".

He said Britain and France, the third and fourth largest military spenders in the world, showed a "willingness and a capability" to play a role on the global stage.

The treaty was "based on pragmatism, not just sentiment", said Cameron, who added that the treaty would be welcomed by the United States, which is Britain's global strategic partner, as it represented European nations cooperating on military issues.

The treaty was "about practical, hard-headed cooperation between two sovereign nations," said Cameron, who was keen to emphasis that neither nation was giving up sovereignty over its armed forces. "Britain and France, are and will always remain sovereign nations able to deploy armed forces independently."

France had been part of NATO but its troops had been separate from NATO's command structure for more than 40 years, when Sarkozy brought France back fully into NATO in 2009, and Cameron praised this move.